It has been proposed to use plastics film as the membrane through which heat is to be transferred between fluids in a heat exchanger because, compared with the metals which are conventionally used, it is inexpensive, resistant to corrosion and comparatively easy to replace.
The low price of polyolefin and polyester films makes them attractive for this use, but they suffer from the fact that their surfaces are not naturally wettable. This means that heat transfer coefficients are reduced because liquids flowing over the surfaces of the film do so as droplets rather than as the desired liquid film. Various treatments have been given to polyethylene film in particular to make it more wettable, including subjecting it to ionising radiation from a corona discharge and coating it with silica, but to our knowledge this has not resulted in any treated films which combine cheapness with retention of wettability over extended periods of use.